1. Field of the Invention
The present invention relates to a method for manufacturing monolithic electronic components, and in particular relates to an improved method in which plural ceramic green sheets are stacked on top of one another.
2. Description of the Related Art
When monolithic ceramic electronic components such as monolithic ceramic capacitors are manufactured, the following steps are often followed: preparing a mother green sheet with inner conductors printed thereon in a state backed with carrier film; cutting off a ceramic green sheet having a predetermined size from the mother green sheet; peeling off the ceramic green sheet having the predetermined size from the carrier film; and stacking the ceramic green sheets peeled off from the carrier film one on top of the other.
A manufacturing apparatus 1, part of which is shown in detail in FIG. 3, is used to manufacture monolithic ceramic electronic components by using ceramic green sheets as mentioned above.
The manufacturing apparatus 1 comprises a cutting table 4 for positioning a mother ceramic green sheet 3, backed with a carrier film 2 (FIG. 3), via the carrier film 2. On the surface of the mother green sheet 3, inner conductors, such as inner electrodes (not shown), are printed in a distributed pattern.
The carrier film 2 and the mother ceramic green sheet 3 are moved, for example intermittently, along the top surface of the cutting table 4. A plurality of suction ports (not shown) are disposed on the cutting table 4 for applying a negative pressure to chuck the carrier film 2 by vacuum chucking, so as to position the carrier film 2 relative to the cutting table 4.
A cutting blade 5 is located above the cutting table 4 and is movable toward and away from the cutting table 4, so that a ceramic green sheet 6 having a predetermined size is cut off from the mother ceramic green sheet 3 by the cutting blade 5 (see FIG. 3).
A chuck head 7 is disposed in a space surrounded by the cutting blade 5. The chuck head 7 is movable toward and away from the cutting table 4 with the cutting blade 5. The bottom surface of the chuck head 7 is a holding surface 8 for holding the cut off ceramic green sheet 6. The detail of the holding surface 8 is shown in FIG. 4.
A plurality of vacuum ports 9 and 10 are distributed on the holding surface 8. A negative pressure is applied respectively to each of these ports. The cut off ceramic green sheet 6 is held on the holding surface 8 by the vacuum created by the negative pressure respectively applied thereto through the vacuum ports 9 and 10. The vacuum ports 9 and 10 are classified into central vacuum ports 9 located in the central portion of the holding surface 8 and peripheral vacuum ports 10 located at the peripheral portion thereof. As shown in FIG. 4, the peripheral vacuum ports 10 are preferably disposed with a higher density than that of the central vacuum ports 9 to hold the ceramic green sheet 6 more strongly in the peripheral portion.
The manufacturing apparatus 1 operates as follows.
First, the cutting blade 5 descends with the chuck head 7 until the cutting blade 5 cuts a ceramic green sheet 6 having a predetermined size from the mother ceramic green sheet 3. To achieve this result, the edge of the cutting blade 5 protrudes from the holding surface 8 of the chuck head 7 at least during the step of cutting. The degree of protrusion is chosen so as to protrude by a distance which is slightly longer than the thickness of the mother ceramic green sheet 3. The cutting blade 5 does not totally cut the carrier film 2 while it cuts the ceramic green sheet 6 off from the mother ceramic green sheet 3.
When the chuck head 7 descends with the cutting blade 5, the holding surface 8 is brought into contact with the ceramic green sheet 6. At this time, negative pressure is applied to the vacuum ports 9 and 10 to hold the ceramic green sheet 6 onto the holding surface 8. Then the chuck head 7 ascends with the cutting blade 5 to thereby peel the ceramic green sheet 6 off the carrier film 2 and hold the ceramic green sheet 6 on the chuck head 7. The state of this step is shown in the FIG. 3.
Then the chuck head 7 holding the ceramic green sheet 6 is transferred to a position above a depositing table (not shown) located a distance away from the cutting table 4. Next, the chuck head 7 is lowered so as to deposit the ceramic green sheet 6 onto the depositing table. At this time, the ceramic green sheet 6 on the depositing table is pressed slightly with the chuck head 7. By repeating this process (and thereby stacking a plurality of ceramic green sheets 6 one on top of the other on the depositing table), a laminated product formed of a plurality ceramic green sheets 6 is manufactured.
The laminated product is pressed and cut into respective monolithic ceramic electronic components on demand so as to produce raw chips for plural monolithic ceramic electronic components. These raw chips are baked and then external electrodes, etc. are formed thereon, so that desired monolithic ceramic electronic components can be obtained.
With the demand for miniaturizing electronic devices in recent years, miniaturization of monolithic ceramic electronic components used therefor, such as monolithic ceramic capacitors, is also proceeding. As for the monolithic ceramic capacitor in particular, not only miniaturization, but also increased capacity is demanded. In the monolithic ceramic capacitor, an efficient way to increase capacity and miniaturizing is to increase the number of layers while reducing the thickness of a dielectric layer.
Reducing the thickness of the dielectric layer is achieved by reducing the thickness of the mother ceramic green sheet 3 or the ceramic green sheet 6 used in the above-mentioned manufacturing apparatus 1 shown in FIG. 3. In general, the thinner the ceramic green sheet, the more difficult it is to treat. The manufacturing apparatus 1 shown in FIG. 3 has a structure suitable for treating the sheet even when the thickness of the ceramic green sheet 6 is reduced.
However, when the thickness of the ceramic green sheet 6 is reduced to no more than 10 xcexcm, for example, undesired deformation or damage may be generated in the ceramic green sheet 6. More specifically, the ceramic green sheet 6 may be deformed in an area located adjacent the vacuum ports 9 and 10, or it may be damaged in the area where the ceramic green sheet contacts the edge of the vacuum ports 9 and 10. The reasons for these problems are as follows.
FIG. 5 is an exploded sectional view of a single vacuum port, for example one of the central vacuum ports 9, disposed in the chuck head 7.
As described above, holding of the ceramic green sheet 6 with the chuck head 7 is achieved by applying negative pressure to the vacuum ports 9 and 10. Portions 6a of the ceramic green sheet 6 which cover the vacuum ports 9 and 10 are prone to be retracted inside the vacuum ports 9 and 10 as shown in FIG. 5. The degree to which this occurs will be dependent upon the thickness of the ceramic green sheet 6, the sizes of the vacuum ports 9 and 10 and the intensity of the negative pressure. Additionally, since the vacuum ports 9 and 10 are generally formed by drilling or laser working, etc., comparatively sharp edges remain on edges 11 of the vacuum ports 9 and 10 located in the holding surface 8.
For this reason, when the portions 6a of the ceramic green sheet 6 are retracted inside the vacuum ports 9 and 10, undesired deformation is produced in the portions 6a, or in a worse case, the sharp edge 11 cuts into the ceramic green sheet 6 resulting in the damage of the ceramic green sheet 6.
Retraction of the portions 6a of the ceramic green sheet 6 inside the vacuum ports 9 and 10 will not normally be produced while the sheet 6 is backed by carrier film 2. It is likely to occur after the sheet is peeled off the carrier film 2.
The undesired deformation or damage produced in the portion 6a of the ceramic green sheet 6 remains after a plurality of ceramic green sheets 6 are stacked up. FIG. 6 is a partial sectional view of the chuck head 7 and the depositing table 12 showing a plurality of ceramic green sheets 6 stacked one on top of the other.
When inner conductors, such as inner electrodes, are formed on the surface of the mother ceramic green sheet 3 as described above, the ceramic green sheet 6 having a predetermined size is cut off from the mother ceramic green sheet 3 having a predetermined positional relationship relative to the inner conductors. Then in the transferring step, it is necessary to transfer the ceramic green sheet 6 onto the depositing table 12 while maintaining a fixed relationship between the chuck head 7 and the depositing table 12. If there is a gap in the positional relationship between the chuck head 7 and the depositing table 12 during the transferring step, an undesired positional gap between inner conductors arranged on the ceramic green sheets 6 will be generated.
For this reason, in the transferring step, the vacuum ports 9 and 10 of the chuck head 7 are always placed in the same position relative to the deposition table 12. Accordingly, as shown in FIG. 6, the portions 6a of the ceramic green sheets 6, wherein undesired deformation or damage due is produced, are aligned.
The ceramic green sheet 6 on the depositing table 12 is generally pressed slightly with the chuck head 7 as described above. This is done to prevent the occurrence of slippage between deposited (stacked) ceramic green sheets 6 and heat may be applied along with the application of pressure. However, even when such a pressing step is performed, since the vacuum ports 9 or are always positioned in the portions 6a of the ceramic green sheets 6 in which deformation or damage is produced, the application of pressure is not applied to the portions 6a and there is no chance for modifying the undesired deformation or damage. In the worst case, the deformation or the damage may lead to breakage with advancing deposition.
In addition, the laminated product obtained by stacking the plurality of ceramic green sheets 6 is generally pressed again. Modifying of the deformation or the damage described above by this pressing step is not expected.
The laminated product is cut to the size of respective monolithic ceramic electronic components so as to generate raw chips for plural monolithic ceramic electronic components. For that reason, among these chips, all the chips taken from the portions 6a of the ceramic green sheet 6 wherein vacuum ports 9 or 10 are positioned may become defective.
Accordingly, it is an object of the present invention to provide a method for manufacturing monolithic ceramic electronic components capable of solving the above-mentioned problem.
According to the present invention, a method for manufacturing monolithic ceramic electronic components comprises the act of:
(A) cutting a ceramic green sheet having a predetermined size from a mother ceramic green sheet backed with carrier film using a cutting blade;
(B) removing the ceramic green sheet from the carrier film using a chuck having a plurality of vacuum ports distributed on a holding surface of the chuck, the vacuum ports having a negative pressure applied thereto;
(C) stacking the ceramic green sheet on a depositing table using the chuck; and
(D) repeating acts (A) through (C) to deposit successive ceramic green sheets onto the depositing table one on top of the other, the relative positions of the chuck and the depositing table when the chuck deposits first and second successive ceramic green sheets onto the depositing table being shifted with respect to one another so that the vacuum ports of the chuck are not located in the same position relative to the depositing table when the first and second successive ceramic green sheets are laid one on top of the other.
In a preferred embodiment, the act of cutting comprises: positioning the mother ceramic green sheet on a cutting table; and causing relative movement between a cutting blade and the cutting table to cut the ceramic green sheet from the mother ceramic green sheet.
The cutting blade preferably surrounds the chuck.
In the preferred embodiment, for each successive ceramic green sheet deposited on the depositing table, the relative positions of the chuck and the depositing table are shifted so that the vacuum ports of the chuck are, not located in the same position relative to the depositing table when successive ceramic green sheets are laid one on top of the other.
In the preferred embodiment, inner conductors are formed on the mother ceramic sheet in a pattern. The location of each successive ceramic green sheet cut from the mother ceramic green sheet relative to the pattern of the inner conductors formed on the mother ceramic green sheet is shifted by an amount corresponding to the shift of the relative positions of the chuck and the depositing table during successive acts of depositing successive ceramic green sheets one on top of the other.
The invention preferably also includes the act of pressing the successive ceramic green sheets together with the previously deposited ceramic green sheets, the act of pressing being repeated after each successive ceramic green sheet is deposited on top of the previously deposited ceramic green sheets.